This invention relates to an acceleration pump of a carburetor for an internal combustion engine and more particularly to an improvement provided in the acceleration pump for enabling the same to accurately regulate the quantity of additional fuel for acceleration supplied to the engine depending on the ambient temperature.
Nowadays there is a growing need to effect control of the quantity of additional fuel for acceleration supplied to an internal combustion engine, particularly for use in an automotive vehicle, by an acceleration pump of a carburetor in accordance with a change in the ambient temperature. To attain this end, proposals have been made to employ a wax or other heat sensitive element to vary the length of downward stroke of a piston inserted for reciprocatory movement in a cylinder of the acceleration pump so as to thereby regulate the quantity of additional fuel for acceleration discharged by the acceleration pump. One example of the acceleration pump of this type is described in detail in U.S. Ser. No. 841,736 filed by Inoue et al on Oct. 13, 1977, now U.S. Pat. No. 4,157,365.
The acceleration pump device described in the aforesaid application is constructed such that it automatically diminishes the quantity of additional fuel for acceleration supplied to the engine when the ambient temperature rises and increases the quantity of the acceleration fuel when the ambient temperature falls. This device can satisfactorily accomplish the object of regulating the acceleration fuel as has been planned.
However, research further conducted into the engine operating condition and the air-polluting constituents of the exhaust gases of internal combustion engines has revealed that, when the ambient temperature is high, no acceleration fuel need be supplied to the engine until the degree of opening of the throttle valve reaches a certain level and only a small quantity of acceleration fuel need be supplied to the engine even when the throttle valve has been opened widely. In the acceleration pump device referred to hereinabove, the fuel discharging characteristic of the pump is determined irrespective of the ambient temperature, if no fuel is allowed to be discharged by the acceleration pump until the opening of the throttle valve reaches a predetermined level from idling. Thus the aforesaid device is not capable of supplying acceleration fuel in a quantity which is actually required for obtaining smooth acceleration at small throttle opening when the ambient temperature is low.